The application relates generally to the use of magnetic resonance imaging (MRI) data. More specifically, the application relates to the improved visualization of steady-state contrast-enhanced MRI anatomical data with superimposed physiologic data. Most specifically, the application relates to improving the visualization of the arterial and venous blood pools in magnetic resonance angiography (MRA).
Cardiovascular disease is a primary health threat. Therefore, it is essential to detect cardiovascular disease in its early stages. One manner to detect cardiovascular disease is through the use of magnetic resonance angiography (MRA). The primary goal of MRA is to non-invasively acquire necessary clinical information via image data to diagnose and plan treatment for various cardiovascular problems. Unlike the current standard of treatment, X-ray angiography, MRA does not require insertion of a catheter for introduction of the contrast agent. Additionally, X-ray angiography (XRA) contrast agents are nephrotoxic, whereas MRA contrast agents are typically much better tolerated by the body. Although MRA is only beginning to emerge into mainstream clinical practice, it has the potential to become the primary modality to image cardiovascular tissues in the future.
In MRA, the first generation of contrast agents introduced into the clinical market were known as ECF agents. These agents rapidly leave the bloodstream and xe2x80x98leakxe2x80x99 into the fluids in the body, reducing contrast between the blood pool and the rest of the body quickly. Intravascular agents, through a variety of mechanisms, extend the persistence of the contrast agent in the blood pool, allowing for longer image acquisition periods. Until intravascular agents were introduced, MRA image acquisition was typically limited to the first pass of the contrast bolus, much like XRA, due to the extensive leakage of the contrast agent into the extracellular fluid. Intravascular agents remain in the blood pool much longer, allowing for longer MR scan times, greater potential resolution, and less reliance on timing of the introduction of the contrast bolus, etc. This longer persistance in the blood, however, introduces a problem in visualization. Because of simultaneous enhancement of both the arterial and venous blood pools, the vessels obscure each other when using projection methods (such as maximum intensity projection (MIP)), and can potentially confuse the reader even when viewing the source data.
Prior methods for manipulating the visualization of MRA data include segmentation methodologies and Digital Subtraction Angiography (DSA). Each of these methods, however, disadvantageously remove a significant amount of potentially useful information and/or have reliability issues. Additionally, reliance on capturing a contrast bolus delivery (for DSA) can be difficult, or almost impossible (as in carotid imaging). Additionally, DSA has been presented in the past as a method of removing background information, not as a technique for removal or reduction of other vascular structures. These vascular structures, however, also contain potentially relevant diagnostic information. Computer segmentation methods alone allow for the loss of supporting information, such as anatomic landmarks from surrounding anatomy, and exclusion of potentially clinically significant information.
Previous work in the area of angiographic image processing tends to relate to the removal of background information to enhance vessel visibility without removing the high intensity signal that represents the blood pool. U.S. Pat. No. 5,297,551 discloses a method of intensity manipulation. However, a method such as this does not effectively differentiate between the arterial and venous blood pools, which in this case is very desirable.
This task of differentiating between the arterial and venous blood pools is effectively independent of enhancing visibility by manipulating the background regions. Because no contrast agents until the present time would remain in the blood long enough to effectively enhance both blood pools at the same level simultaneously, no previous work is known to have been done to effectively overcome this effect.
U.S. Pat. No. 6,073,042 to Simonetti shows a method of displaying three-dimensional MRA images in which arteries can be distinguished from veins. The Simonetti method, however, requires acquiring multiple image series as a function of time and requires many calculations to find curves that simulate the change of voxel intensity as a function of time. As is the case with most MRA methods, image sets are closely temporally spaced (i.e. short TR) in order to accurately represent dynamic phenomena. Unfortunately, this necessarily limits the resolution of the resultant images compared with images required over longer time periods. There remains a need for MRI techniques that faithfully convey physiological phenomena in images with high spatial resolution. In the case of MRA, there remains a need for techniques which present high resolution images of the vasculature and indicate whether those vessels are arteries or veins.
The invention provides a method of visualizing MRI data taken from two data sets, one set that can comprising high spatial resolution anatomical image data, and the other that can comprise physiological data which is not necessarily of as high a resolution as the other data set. The method then combines the two data sets to produce a clinically useful MR image. The methods disclosed herein are especially useful for improving the visualization of contrast enhanced arterial and venous blood pools in magnetic resonance angiography (MRA). In general, these methods allows for the rapid generation of clinically useful MRA images which appear to have a high spatial resolution and detailed anatomical information while also illustrating arterial-venous differentiation.
In a preferred embodiment, the invention provides methods for improving visualization of contrast enhanced MRA data in which simultaneous enhancement of the artery and vein portions of the circulatory system is present (i.e. the xe2x80x9csteady statexe2x80x9d). The invention mathematically manipulates the relative enhancement of the arterial and venous blood pools to allow differentiation between the two pools without removing either pool from the images. This allows the viewer considerable information retention in the data while also allowing for rapid recognition of the anatomy of interest. This method of problem solving exploits the novel strengths of intravascular contrast in the steady state while removing the difficulty of producing rapid visualization of these data sets.
In accordance with one embodiment of the invention, the method of improving the visualization of magnetic resonance angiography data taken from a patient, generally includes:
providing a display device;
acquiring a first set of data representing a steady state contrast enhancement of an arterial blood pool and a venous blood pool of the patient;
acquiring a single second set of data that, in combination with the first set of data, provides information sufficient to differentiate between the arterial blood pool and the venous blood pool of the patient;
combining intensities in predetermined locations by a predetermined amount of the first and the second sets of data to produce a third set of data representing the arterial and the venous blood pools in comparable resolution with each other; and
displaying the third set of data upon the display device.